WhatsApp users are being urged to update the app immediately because of a security bug that allows hackers to take control of your phone by simply calling it via the app - whether or not you answer.

The spyware installed by the hackers is capable of trawling through calls, texts and other data, switching on the phone's camera and microphone and performing other malicious activities, according to reports.

But is there a foolproof way of knowing if you have been affected by the hack, and what should you do to protect yourself?